Beam failure recovery

1. A method performed by a user equipment (UE), the method comprising:

sending a beam failure recovery request message including information regarding beam failure recovery and information regarding a new candidate beam to a first cell, wherein the information regarding the new candidate beam comprises a reference signal identifier indicating a specific beam as the new candidate beam, and the beam failure recovery request message is a medium access control (MAC) control element (CE);

monitoring, after sending the beam failure recovery request message, a response to the beam failure recovery request message exclusively via the new candidate beam of a second cell; and

receiving the response to the beam failure recovery request message via the new candidate beam from the second cell.

2. The method of claim 1 , wherein the beam failure recovery request message is sent via physical uplink shared channel (PUSCH) or physical uplink control channel (PUCCH) of the first cell.

3. The method of claim 2 , wherein the beam failure recovery request message is sent via PUCCH of the second cell before it is sent via PUSCH or PUCCH of the first cell.

4. The method of claim 1 , wherein the beam failure recovery request message is sent via one of physical uplink shared channel (PUSCH) of the first cell, physical uplink control channel (PUCCH) of the first cell and PUCCH of the second cell.

5. The method of claim 1 , wherein the MAC CE is scheduled in a priority higher than other uplink transmissions.

6. The method of claim 1 , wherein the response is monitored via a same beam as the new candidate beam from sending the beam failure recovery request message for a predetermined time period.

7. The method of claim 1 , wherein physical downlink control channel (PDCCH) is monitored in a predefined control resource set (CORESET).

8. The method of claim 1 , further comprising receiving, via physical downlink shared channel (PDSCH), transmission configuration indicator (TCI) state information in a radio resource control (RRC) configuration message.

9. The method of claim 1 , wherein the response is a control resource set (CORESET) resource preconfigured for beam recovery sent via physical downlink control channel (PDCCH).

10. The method of claim 1 , wherein the first cell is primary cell or primary-secondary cell and the second cell is secondary cell.

11. The method of claim 1 , wherein the first cell is secondary cell and the second cell is primary cell or primary-secondary cell.

12. The method of claim 11 , before sending the beam failure recovery request message via a working beam of the primary cell or primary-secondary cell, further comprising:

sending a random access procedure signal via random access procedure resource of the primary cell or primary-secondary cell; and

configuring the working beam of the primary cell or primary-secondary cell.

13. A method performed by a base station, the method comprising:

receiving a beam failure recovery request message including information regarding beam failure recovery and information regarding a new candidate beam, wherein the information regarding the new candidate beam comprises a reference signal identifier indicating a specific beam as the new candidate beam, and the beam failure recovery request message is a medium access control (MAC) control element (CE); and

sending, after receiving the beam failure recovery request message, a response to the beam failure recover request message exclusively via the new candidate beam.

14. The method of claim 13 , wherein the beam failure recovery request message is received via physical uplink shared channel (PUSCH) or physical uplink control channel (PUCCH).

15. The method of claim 13 , wherein the response is sent in a control resource set (CORESET) resource preconfigured for beam recovery via physical downlink control channel (PDCCH).

16. The method of claim 13 , wherein the beam failure recovery request message is received via a working beam of a first cell.

17. The method of claim 13 , wherein the beam failure recovery request message is received from another cell.

18. A user equipment (UE), comprising:

at least one memory; and

at least one processor coupled with the at least one memory and configured to cause the UE to:

send a beam failure recovery request message including information regarding beam failure recovery and information regarding a new candidate beam to a first cell, wherein the information regarding the new candidate beam comprises a reference signal identifier indicating a specific beam as the new candidate beam, and the beam failure recovery request message is a medium access control (MAC) control element (CE);

monitor, after sending the beam failure recovery request message, a response to the beam failure recovery request message exclusively via the new candidate beam of a second cell; and

receive the response to the beam failure recovery request message via the new candidate beam from the second cell.

19. The UE of claim 18 , wherein the beam failure recovery request message is sent via physical uplink shared channel (PUSCH) or physical uplink control channel (PUCCH) of the first cell.

20. A base station, comprising:

at least one memory; and

at least one processor coupled with the at least one memory and configured to cause the base station to:

receive a beam failure recovery request message including information regarding beam failure recovery and information regarding a new candidate beam, wherein the information regarding the new candidate beam comprises a reference signal identifier indicating a specific beam as the new candidate beam, and the beam failure recovery request message is a medium access control (MAC) control element (CE); and

send, after receiving the beam failure recovery request message, a response to the beam failure recover request message exclusively via the new candidate beam.